The present invention relates to medical electrodes used as indifferent electrodes in electrosurgical procedures, and more particularly to a capacitively coupled electrode having improved convenience, safety, and performance.
In electrosurgical procedures, an electrosurgical generator generates high radio frequency electric current which is fed to an active electrode. The active electrode is used to cut tissue and coagulate blood vessels and is activated for relatively short times during such procedures. An indifferent, or patient, electrode is placed in contact with a patient to provide a return path for the high frequency current to the generator, which is in turn typically connected directly to ground or to an isolated ground unit.
The input current is applied to the tissue by means of the active electrode which is preferably of small cross-section so that high current densities may be obtained at the surgical site. These high current densities provide the required heating (up to 1,000.degree. C. at the point of contact) needed for the operating procedure. However, it is essential that the indifferent electrode have contact over sufficient surface area of the patient to insure that the return current has a low density to avoid burning or scarring of the patient's tissue which is in contact with the indifferent electrode.
Prior art indifferent electrodes have either been of the direct electrical contact type or of the capacitively coupled type. Direct electrical contact type indifferent electrodes have either been designed to be attached directly to or placed underneath a patient and have been available in both dry (direct metal contact to skin) and conductive gel or adhesive (electrode coupled to skin through a conductive solution, gel, or polymer) forms. However, direct electrical contact type electrodes suffer from a variety of problems. For example, if a pregelled form is used, the gel may have dried out prior to use or may dry out during surgical use, there may be bacterial growth in the gel, and there are patient clean-up problems in removing the gel after surgery. Additionally, the gel may cause skin irritation in some patients.
If a dry form direct electrical contact type electrode is utilized, usually in the form of a large surface area metal plate or foil, other problems arise. These include the possibility of burns caused by preferential current flow due to patient perspiration or spilled fluids at the contact site, burns caused by the movement of the patient during surgery which breaks contact with a substantial portion of the metal surface, and electrical hazards to physicians and other operating room personnel if a protruding edge of the metal electrode is accidently touched or comes in contact with other metal surfaces in the operating room.
Moreover, all previous types of direct electrical contact type indifferent electrodes suffered from hot spots around their leading edges caused by a preference of radio frequency electrical current to leave a patient's body at those points. This uneven current distribution through the electrodes accentuates possible patient burning or scarring problems.
Capacitive coupled electrodes, on the other hand, have the potential of being much safer in use. These types of electrodes have a dielectric material sandwiched between the metal electrode and the patient's skin. In the past, these electrodes have been held in position on a patient's skin by elastic bands, strips of adhesive tape, or a peripheral adhesive area around the edges of the capacitor structure. However, these prior art methods of securing the electrode to the patient are unreliable. If a patient is moved or repositioned, air gaps or tenting causes portions of the dielectric material to pull away from a patient's skin, creating hot spots and possibly causing burning or scarring of tissue. Accordingly, the need still exists in the art for a convenient, safe, and reliable indifferent electrode for use in electrosurgical procedures.